This invention relates to an optical aligning apparatus of liquid crystals (LCs), and more particularly to an apparatus and a method for optically aligning LCs in a desired direction through control of the polarization direction of light.
To fabricate liquid crystal displays (LCDs) having uniform brightness and high contrast ratio, it should align LC molecules injected between upper and lower glass substrates in a constant direction. It is in general LCDs that LC molecules has been aligned in a constant direction through alignment films which are respectively formed on opposite surfaces of the upper and lower glass substrates. There have been used a conventional rubbing method and an UV alignment method as LC alignment techniques using alignment films. The conventional rubbing method which now is the most widely used as alignment techniques, aligns LCs with linear grooves formed in alignment films in a constant direction. In rubbing methods, polyimide as alignment films is coated on a transparent glass substrate of LCD and rubbed with a rubbing cloth in a constant direction, resulting in inducing physical defects on the surface of the polyimide to form linear grooves.
The UV alignment technique which utilizes polarized light differently from the mechanical rubbing technique, forms polyvinyl resin on a transparent glass substrate of an LCD and irradiates UV light to it, resulting in aligning LCs.
The conventional rubbing method has difficulties in adjusting a pretilt angle and achieving the reproducibility of process. Because the conventional rubbing method forms and rubs with a rubbing cloth polyimide on the surface of the glass substrate where TFT arrays or color filter arrays are arranged, it causes electrical and mechanical damages to the underlying TFT arrays and reduces the life time of LCDs due to particles and static electricity generated in rubbing. The UV alignment methods have difficulties in controlling residuum in polymerization by irradiation of UV light and fabricating uniform alignment films.
In Korean Patent Application No. 96-42514, there is disclosed an alignment method of "Method for aligning polymeric film, LC alignment method using the same, LC cell and fabrication thereof" to solve the problems of the conventional rubbing method and the UV alignment method.
To briefly speaking, the polymeric film alignment method forms the polymeric film doped with the photosensitive compound on a transparent glass substrate and irradiates the circularly polarized light to the polymeric film, resulting in tiltly aligning photosensitive compound with respect to the substrate surface. By using the polymeric alignment film, it is able to tiltly align LCs injected between two glass substrates with tilt alignment of the photosensitive compound contained within the polymeric alignment film. In the polymeric film alignment method, azo dye doped-polymeric alignment film was used for the photosensitive compound and circularly polarized beam was used for the irradiating light to the polymeric film instead of linearly polarized beam.
In order to align LCs using the above polymeric alignment film, there is a urgent need for an optical apparatus that polarizes beam from the light source into circularly polarized beam or elliptically polarized beam and irradiates the polarized light to the polymeric alignment film.